Frontier: Pure Oxygen Can Harm the Brain

Physicians rushing to get much-needed oxygen to a patient in a medical emergency commonly prescribe pure oxygen. But a new study suggests the therapy may trigger a release of chemicals that actually make it harder for the heart to deliver oxygen.

A team at the University of California, Los Angeles, led by neurobiologist Ronald Harper, examined functional magnetic resonance imaging (fMRI) of brain activity in 14 healthy children ages 8 to 15 as they inhaled normal air, 100 percent oxygen and a mixture of 95 percent oxygen and 5 percent carbon dioxide.

After the children breathed pure oxygen, researchers recorded increased activity in the hippocampus and hypothalamus. The oxygen–carbon dioxide mix caused far less activity, and in some cases none at all, according to the study, published in May in Public Library of Science (PLoS) Medicine.

“Several brain areas responded to 100 percent oxygen by kicking the hypothalamus into overdrive,” Harper says. “The hypothalamus overreacted by dumping a massive flood of hormones and neurotransmitters into the bloodstream. These chemicals interfere with the heart’s ability to pump blood and deliver oxygen—the opposite effect you want when you’re trying to resuscitate someone.”

The researchers say that pure oxygen causes patients to breathe more quickly, causing the rapid exhalation of carbon dioxide. The drop in carbon dioxide in the blood constricts blood vessels, restricting the flow of oxygen to vital tissues throughout the body. Adding carbon dioxide to oxygen seemed to solve this problem.

Harper’s team plans to study the long-term effects of pure oxygen and whether the brain response is different when a patient is sleeping. But for now, the researchers say they encourage physicians to add carbon dioxide to oxygen when treating patients, especially when resuscitating infants or giving oxygen for extended periods of time.